The invention relates to a locking device having a lock cylinder and a matching key; the key having a key bit with at least one coding notch cut in, in particular on the front, and a blocking rib that runs in the direction of extent of the key bit and has at least one blocking rib indentation; the lock cylinder having a housing with a bearing bore and a cylinder core that is mounted in the bearing bore and has a keyway for insertion of a key, the cylinder core being blocked against rotation, when a key is not inserted, by at least one housing pin mounted in a housing hole; the housing pin projecting into a core hole of the cylinder core in which a core pin is fitted, and the housing pin being able to be brought into a release position enabling rotation of the cylinder core by entry of the core pin into the coding notch of the key inserted into the keyway; and the locking device having a blocking member for sensing the blocking rib indentation, the blocking member engaging, when a blocking rib indentation is not present, in a blocking recess of the bearing bore and preventing rotation of the cylinder core.
EP 0 851 079 A1 describes a lock cylinder having a cylinder core into the keyway of which a flat key can be inserted, the key having a blocking rib which can be sensed by an inverted pin. The inverted pin disposed in the cylinder core interacts with a counter-pin disposed in the cylinder housing, so that the cylinder core is blocked against rotation by this blocking device when the height of the rib is less or greater than the proper rib height. The rib is here sensed on its side wall.
WO 2000/022262 describes a lock cylinder and a key that is matched thereto, the key bit of the key having, on one of its two broad sides, a blocking rib, and indentations on the opposite broad side. The indentations are sensed by blocking members. If the indentation is missing, the blocking members block in the event of rotation of the cylinder core. The blocking rib is sensed by a slide. If the blocking rib is missing, the slide can be displaced so that a capturing opening disposed immediately beside the core hole is made available into which a housing pin can enter if there is partial rotation of the cylinder core, so that the cylinder core cannot be rotated further.
DE 198 38 000 A1 describes a locking device of the generic kind having a lock cylinder and a key matched thereto. The key has a multiplicity of coding notches cut in at the front by which core pins mounted in core holes in the cylinder core can be organised in such a way that the interface between housing pin and core pin lies in the sleeve surface of the housing bore. Openings run transversely to the keyway in each of which blocking pins are disposed. These blocking pins sense blocking rib indentations of a blocking rib that extends in the direction of extent of the key bit. If a blocking rib indentation of this kind is not present, a blocking portion of the blocking member then lies in a blocking recess in the housing, so that the cylinder core cannot rotate despite the tumbler pins being correctly positioned. A lock cylinder of this kind can be tampered with by filing down the blocking rib.
It is an object of the invention to improve the security against tampering of a lock cylinder of the generic kind.